Relative lmportance of GCA and SCA in Genstic Breeding of Chinese fir

Two types of parents of Chinese fir with different genetic properties were adopted for mating design and field test: 9×9 half diallel cross and 6×6 complete diallel cross were made respectively. The results of the combining ability analysis indicated: when genetic test was carried out by using material Ⅱ (cross parents were rapid growth clones through evaluation and selection of GCA in growth traits), its population variances of GCA (general combining ability) σg2σs2 population variances of SCA (special combining ability). But when genetic test was carried out by using material Ⅰ (parents clones from plus tree to be studied), σg2σs2. The experimental results in different tests were opposite, which was determined by the properties of material being studied. In the field of genetic improvement of Chinese fir, additive theory (additive genetic variance plays a leading role in controlling character inheritance) and dominant theory (dominant genetic variance plays a leading role) were not contradictory, the reason causing the phenomenon was because test and selection of GCA was in a state of independence of those of SCA.